TBD4

Examples of meiotic drive, the non-Mendelian segregation of a specific genomic region, have been identified in several eukaryotic species.  Maize contains the Abnormal chromosome 10 (Ab10) drive system that transforms typically inert heterochromatic knobs into centromere-like domains (neocentromeres) that move rapidly poleward along meiotic spindles, and are preferentially transmitted to female progeny.  The multi-component meiotic drive system lies within a large haplotype at the end of chromosome 10L.  Ab10 is thought to be responsible for driving the evolution and maintenance of all knob repeats in maize, which can make up as much as 8% of the maize genome.  Knobs can be made of two different tandem repeat sequences (TR-1 and 180 bp), and both repeats have become widespread in Zea species.  The neocentromere activity of TR-1 and 180 bp repeats are controlled separately by sequence-specific factors that map to different regions of the Ab10 haplotype.  Over a period of years we have developed a collection of mutants that are defective in meiotic drive, and shown that each of the mutants are also defective in neocentromere activity of the major 180 bp repeats.

Recent results using multiple sequencing technologies have now given us the first molecular glimpses of Ab10.  The transacting factor that causes neocentromere activity of 180 bp repeats and meiotic drive is located in a small distal tip region of the haplotype.  This region contains numerous ancient pseudogenes and a meiotically expressed C-terminal kinesin protein of the type predicted to move cargo poleward on the spindle.  The kinesin is truncated and contains a divergent N-terminal domain that may be a DNA-binding region.  One of our meiotic drive mutants is an epimutation of this gene, strongly suggesting that we have identified a key “neocentromere gene”.